The present invention relates generally to an improved condition-responsive means for electrically sensing the degree of exhaustion of a cation exchange column or other type of apparatus adapted to treat hard or mineral-containing water, ionized water or for filtering particulates from turbid water. Such water conditioning systems are, of course, relatively widely employed for water treatment, both on an industrial as well as a residential basis.
In the past, a wide variety of systems and techniques have been employed to detect the condition of a resin bed, such as those employed in ion exchange columns or to detect that a filter media needs replacement. These prior art systems typically employ a Wheatstone bridge circuit which, when becoming unbalanced, will trigger a mechanism to actuate the regeneration of the portion of the system which becomes exhausted during use. In the case of a water softener, saturated brine solutions are employed to achieve this regeneration. For example, in residential softeners, a brine tank is employed which has saturated sodium chloride as the active ingredient. The sodium is exchanged for the cations normally contributing to the hardness of the water supply during the softening process. Such cations are typically calcium and magnesium, along with others, such as iron or the like.
To detect the condition of the resin bed disposed in the ion exchange column, electrical sensors, such as spaced-apart probes have been employed in the past. Among the problems typically encountered in the use of such probes are the surface coating thereof by water-borne contaminants, or, alternatively, the electrolytic decomposition of the probe due to the imposition of electrical energy into the system through the probe. Whenever DC current is employed, electrolytic decomposition of the probes become a major concern.
To avoid such decomposition, carbon probes have been proposed in the past. Carbon probes, unfortunately, have been found to become coated or plated with certain of the metal ion constituents of the water supply, and thus change or drift with time so as to become relatively ineffective.
In many of the prior art devices, the objectives or goals of the system are accomplished by a change in conductivity of the ion exchange column, particularly between a spent portion of the column as compared to an unspent or unexhausted portion of the column. Resistivity measurements have been employed as a means of determining the condition of the column, and problems have arisen in finding an effective means for detecting and/or determining resistivity measurements in such an environment over extended periods of time. The present invention, however, achieves the goal of long-term detection, without suffering from problems of electrode probe contamination or electrolysis deterioration.
Certain prior art water treatment regeneration systems are temperature sensitive. That is to say, a triggering event may not be due solely to the movement of the hardness front through the column, but also by the passage of a temperature front. Where, for example, a water softener bed is located in an out-of-doors tank in a hot climate, when water is drawn through the tank, the cold water front propagates through the bed and can cause an unbalancing of the detector electronics to initiate a regeneration cycle when none is required.